1. Field of the Invention
The present invention relates to a peptide that is derived from the MUC-1 gene, by which peptide a HLA-A2-restricted immune reaction against tumor cells can be triggered.
2. Description of Related Art
In an abstract to a lecture held on the 40. annual meeting of the American Society of Hematology, 1998, Brossart et al. show the possibility of deriving such a peptide from the MUC-1 gene, however, without mentioning the sequence of a peptide they tested or the localization of the sequence of a peptide that is not derived from the tandem repeat range of MUC-1.
Peptides for triggering an immune reaction against tumor cells are mentioned, for example, also in the publication by Finn, O. J., et al., (1995) “MUC-1 Epithelial Tumor Mucin-Based Immunity and Cancer Vaccines”, Immunol Rev 145, pages 61-89, but without mentioning sequence information either.
By an immune reaction, for example the destruction of cells by such T cells that are also designated as cytotoxic T cells due to their ability to kill other cells is to be understood. In order to trigger such an immune reaction by cytotoxic T cells, foreign proteins e.g. as a result of a virus infection must be presented to the T cells by a MHC molecule on the cell surface.
These MHC molecules are peptide receptors which usually bind peptides within the cell in order to transport them to the cell surface, where the complex of peptide and MHC molecule can be recognized by T cells. In normal cells, the peptides bound by MHC molecules are derived from the usual cell-owned proteins. During their differentiation in an organism, T cells become tolerant against complexes of own peptides having own MHC molecules. Thus, each new peptide which comes up later, e.g. a peptide which is produced by a cell because of the infection with a virus, can be recognized by T cells.
There are two classes of MHC molecules, whereas those interacting with cytotoxic T cells belong to class I. Classic human class I molecules are HLA-A, B and C, wherein HLA-A2 represents a subclass of the HLA-A molecules.
If the accomplishment of an immune reaction is dependent on the existence of a certain MHC molecule, for example HLA-A2, this is said to be an MHC-restricted, e.g. a HLA-A2-restricted immune reaction. There are also sporadic T cell reactions which take place independently of MHC molecules. These are said to be MHC-unrestricted immune reactions.
In the publication by Finn et al. mentioned at the outset, for the treatment of a tumor patient it was suggested to trigger such a MHC-unrestricted immune reaction against a glycoprotein that is coded by the gene MUC-1 and exists on the surface of cells. The objective is herein to generate an effective immune response with a life-long immunity.
The protein coded by the gene MUC-1, which protein is also called MUC-1, is in most cases polarizedly expressed by normal epithelial cells such that it is normally not accessible for the immune system, like e.g. in the bowel, where it is expressed on the apical side of the epithelial cells, i.e. projecting into the bowel lumen.
However, MUC-1 is not polarizedly expressed on tumor cells, but covers all of the cell. The level of the expression is higher for tumor cells than for normal cells, but for tumor cells the molecules are not completely glycosylated, i.e. the side chains of saccharine molecules comprise a shortened structure with respect to MUC-1 that is produced by healthy cells. The incomplete glycosylation results in epitopes on the protein portion of MUC-1, which epitopes usually exist masked by saccharine side chains and are accessible on tumor cells for the immune system. Thus, the immune system can distinguish between this underglycosylated MUC-1 and the normal not underglycosylated MUC-1.
Beside the side chains made of saccharine molecules, another essential structure feature are the so-called tandem repeats. These are sequences of 20 amino acid residues which are each repeated in an identical or similar manner approximately 20 to 125 times in the MUC-1 molecule.
For triggering an effective immune reaction by T cells, co-stimulators are required, whereto do belong in particular the so-called dendritic cells which take up proteins presented from outside and can present them after their processing to peptides so that cytotoxic T cells can be activated thereby. Therefore, Finn et al. suggest to inject synthetic peptides which represent the MUC-1 tandem repeats, together with an adjuvans that attracts dendritic cells. An adjuvans is a substance which, when injected together with a substance against which an immune reaction is to be triggered, strengthens the response of the immune system to this substance in an unspecified manner. By such a vaccination, an MHC-unrestricted T cell reaction against the tandem repeats shall be obtained. It is even suggested to replace amino acids which can mediate a MHC-class-I-binding in the synthetic peptides by others so that no MHC-restricted T cells can arise by a presentation of the peptides by MHC class I molecules.
On the one hand, the problem of a possible autoimmunity can be reduced by avoiding an MHC-restricted immune response, on the other hand, the lower efficiency of an MHC-unrestricted immune response in comparison to an MHC-restricted one is a great disadvantage. Thus, the chances are also lower to make a tumor to disappear by means of an MHC-unrestricted immune response than by means of an MHC-restricted immune response.
For this reason, on the occasion of the presentation mentioned at the outset, the inventors of the present application have suggested to trigger a MHC-restricted immune response against MUC-1 expressing cells. They report that to this end the known MUC-1 amino acid sequence has been searched for HLA-A2 binding motives by means of a computer analysis. Peptides with a high binding probability were identified, synthesized and examined with respect to the regard whether they can induce cytotoxic T cells in vitro with the help of dendritic cells. The cytotoxic T cells created in that way developed an antigen-specific HLA-A2-restricted cytotoxic activity against these target cells that had been incubated before with the respective peptide by which the cytotoxic T cells were activated, or against MUC-1 expressing tumor cells.